Colloidal synthesis of ternary copper indium diselenide quantum dots and their optical properties

Ternary direct semiconductor CuInSe2 quantum dots (QDs) with average particle sizes ranging from 1.2 to 5.6 nm have been synthesized by a colloidal route using commercially available materials. The size-dependent optical band gap and photoluminescence (PL) band shift due to the quantum size effect were successfully observed. The optical band gap evaluated from the optical absorption spectra was varied from 1.48 eV for the 5.6-nm QDs to 1.66 eV for the 1.2-nm QDs. In the PL spectra, the wavelength of the emission band varied from 918 to 838 nm corresponding to the crystal size variation from 5.6 to 1.2 nm. Because the PL band showed a large Stokes shift above 100 meV, the origin of the PL band was related to the electronic transition via defect levels. Based on the slightly In-rich composition of the QDs and the comparatively large increase in energy of the PL band with decreasing crystal size, the emission was suggested to be due to the recombination between electrons in the quantized conduction band and holes in the copper vacancy acceptor.